The spinal column of bones is a highly complex anatomical structure that includes over 20 bones coupled to one another, housing and protecting critical elements of the nervous system having innumerable peripheral nerves and circulatory bodies in close proximity. Despite its complexity, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction. The more than 20 discrete bones of an adult human spinal column are anatomically categorized as one of four classifications—cervical, thoracic, lumbar, or sacral—and are coupled together sequentially to one another by a tri-joint complex that consists of an anterior disc and two posterior facet joints. The anterior discs of adjacent bones are cushioned by cartilage spacers referred to as intervertebral discs or vertebrae. The cervical portion of the spine comprises the top of the spine up to the base of the skull and includes the first seven vertebrae. The intermediate 12 bones are thoracic vertebrae, and connect to the lower spine comprising the 5 lumbar vertebrae. The base of the spine comprises sacral bones, including the coccyx. With its complex nature, however, there is also an increased likelihood that surgery may be needed to correct one or more spinal pathologies.
Various systems exist for connecting fastener elements (e.g., pedicle screws) to bones for the purposes vertebral fixation. Such systems may use a plurality of bone screws fitted in saddles, wherein a plurality of saddles are aligned using a mounting rod. Alignment of mounting rods through positionally fixed saddles may be challenging. If a saddle is not in an appropriate position or an aligned position, the bone screw may have to be removed or repositioned, or the saddle may have to be refitted. In some situations, the mounting rod may have to be bent to align with the saddle at a fixed position. In some situations, additional components, such as offset connectors, may have be introduced to a bone screw system, such that a series of saddles may be aligned and secured by a mounting rod.